Cyclic process for producing taurine

ABSTRACT

There is disclosed a process for producing taurine from ammonium isethionate by the ammonolysis of alkali isethionate in the presence of alkali ditaurinate or alkali tritaurinate, or their mixture, to inhibit the formation of byproducts and to continuously convert the byproducts of the ammonolysis reaction to alkali taurinate. Alkali taurinate is reacted with ammonium isethionate to obtain taurine and to regenerate alkali isethionate. The production yield is increased to from 90% to nearly quantitative. The ammonolysis reaction is catalyzed by alkali salts of hydroxide, sulfate, sulfite, phosphate, or carbonate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.15/268,071, filed on Sep. 16, 2016, which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a cyclic process for the production oftaurine from ammonium isethionate in a high overall yield (i.e., greaterthan 90% to nearly quantitative) by carrying out the ammonolysisreaction of alkali isethionate to alkali taurinate in the presence of amixture of alkali ditaurinate and alkali tritaurinate, followed byreacting with ammonium isethionate.

BACKGROUND OF THE INVENTION

Taurine can be referred to as 2-aminoethanesulfonic acid and is one ofthe amino sulfonic acids found in the tissues of many animals. Taurineis an extremely useful compound with beneficial pharmacological effects,such as detoxification, fatigue-relief, and nourishing and tonifyingeffects. As a result, taurine finds wide applications as an essentialingredient for human and animal nutrition.

Taurine is currently produced in an amount of over 50,000 tons per yearfrom either ethylene oxide or monoethanolamine. At the present time,most taurine is produced from ethylene oxide, following a three-stepprocess: (1) the addition reaction of ethylene oxide with sodiumbisulfite to yield sodium isethionate; (2) the ammonolysis of sodiumisethionate to yield sodium taurinate; (3) the neutralization with anacid, i.e., hydrochloric acid and, preferably, sulfuric acid, togenerate taurine and inorganic salts.

Although the ethylene oxide process is well established and widelypracticed in commercial production, the overall yield is not very high,less than 80%. Moreover, the process generates a large waste stream thatis increasingly difficult to dispose of.

The first stage of the ethylene oxide process, the addition reaction ofethylene oxide with sodium bisulfite, is known to yield sodiumisethionate in high yield, practically quantitative, as disclosed inU.S. Pat. No. 2,820,818 under described conditions.

Therefore, the problems encountered in the production of taurine fromthe ethylene oxide process arise from the ammonolysis of sodiumisethionate and from the separation of taurine from sodium sulfate

U.S. Pat. No. 1,932,907 discloses that sodium taurinate is obtained in ayield of 80%, when sodium isethionate undergoes ammonolysis reaction ina molar ratio of 1:6.8 for 2 hours at 240 to 250° C. U.S. Pat. No.1,999,614 describes the use of catalysts, i.e., sodium sulfate, sodiumsulfite, and sodium carbonate, in the ammonolysis reaction. A mixture ofsodium taurinate and sodium ditaurinate is obtained in a yield as highas 97%. However, the percentage for sodium taurinate and sodiumditaurinate in the mixture is not specified.

DD219023 describes detailed results on the product distribution of theammonolysis reaction of sodium isethionate. When sodium isethionateundergoes the ammonolysis reaction with 25% aqueous ammonia in a molarratio of 1:9 at about 280° C. for 45 minutes in the presence of sodiumsulfate and sodium hydroxide as catalyst, the reaction products comprise71% of sodium taurinate and 29% of sodium di- and tritaurinate.

WO01/77071 is directed to a process for the preparation of ditaurine byheating an aqueous solution of sodium taurinate at a temperature of 210°C. in the presence of a reaction medium. A mixture of sodium taurinateand sodium ditaurinate is obtained.

It is therefore concluded from the foregoing references that theammonolysis of sodium isethionate invariably yields a mixture of sodiumtaurinate, sodium ditaurinate, and sodium tritaurinate. The percentageyield of sodium taurinate has not been more than 80%.

In order to obtain taurine from sodium taurinate, U.S. Pat. No.2,693,488 discloses a method of using ion exchange resins involving astrongly acid ion exchange resin in hydrogen form, and then an anionexchange resin in basic form. This process is complicated and requiresthe use of a large quantity of acid and base to regenerate the ionexchange resins in each production cycle.

On the other hand, CN101508657, CN101508658, CN101508659, andCN101486669 describe a method of using sulfuric acid to neutralizesodium taurinate to obtain a solution of taurine and sodium sulfate.Crude taurine is easily obtained by filtration from a crystallinesuspension of taurine after cooling. However, the waste mother liquorstill contains taurine, sodium sulfate, and other unspecified organicimpurities, which are identified as a mixture of sodium ditaurinate andsodium tritaurinate.

U.S. Pat. No. 9,428,450 and U.S. Pat. No. 9,428,451 overcome some of theproblems in the known ethylene oxide process by converting thebyproducts of the ammonolysis reaction of alkali isethionate, alkaliditaurinate and alkali tritaurinate, into alkali taurinate. The overallyield of the cyclic process for producing taurine from sodiumisethionate is increased to from 85% to nearly quantitative.

U.S. Pat. No. 8,609,890 discloses a process of using isethionic acid orsulfur dioxide to neutralize alkali taurinate to producing taurine andto regenerate alkali isethionate. U.S. Pat. No. 9,108,907 furtherdiscloses a process of using isethionic acid prepared from ethanol toneutralize alkali taurinate to regenerate alkali isethionate. The aim isto reduce or eliminate the use of sulfuric acid as an acid agent in theproduction of taurine.

U.S. Pat. No. 9,061,976 discloses an integrated production scheme byusing sulfur dioxide as an acid and by converting the byproducts of theammonolysis reaction, alkali ditaurinate and alkali tritaurinate, toalkali taurinate. The overall production yield is increased to greaterthan 90% and alkali sulfate is eliminated from the production process.One drawback of this process is the use of gaseous sulfur dioxide, whichimparts a slight smell on the product. Another significant drawback isthat the taurine product from this process may contain trace amount ofalkali sulfite which could be an allergen for certain people.

Copending U.S. Ser. No. 15/238,621 discloses a cyclic process forproducing taurine from isethionic acid in a high overall yield ofgreater than 90% to nearly quantitative, while generating no inorganicsalt as byproducts. However, the starting material, isethionic acid, isdifficult to obtain commercially and is produced by a costly process ofbipolar membrane electrodialysis of alkali isethionate.

CN 101717353A describes a process of preparing taurine by (1) reactingethylene oxide with ammonium sulfite to yield ammonium isethionate andammonia; (2) ammonolysis of the obtained product to ammonium taurinate;(3) acidifying with sulfuric acid to afford taurine. However, repeatedattempts fail to produce any taurine under disclosed conditions.

It is an object of the present invention to overcome the disadvantage ofthe known processes for the production of taurine and to provide, inaddition, advantages, which will become apparent from the followingdescription.

It is another object of the present invention to disclose a process forthe production of taurine from ammonium isethionate in a high overallyield (i.e., greater than 90% to nearly quantitative) without generatingany inorganic salt as byproduct.

The starting material, ammonium isethionate, can be readily andeconomically produced by reacting ethylene oxide with ammonium bisulfiteaccording to prior art, e.g., U.S. Pat. No. 5,646,320 and U.S. Pat. No.5,739,365.

According to the process of the present invention, a solution of alkaliisethionate or regenerated alkali isethionate, alkali ditaurinate, andalkali tritaurinate is mixed with an excess ammonia and is subjectedcontinuously to the ammonolysis reaction to form a mixture of alkalitaurinate, alkali ditaurinate, and alkali tritaurinate, in the presenceof one or more catalysts. After ammonium isethionate is added to theammonolysis solution, excess ammonia is removed to obtain a crystallinesuspension of taurine in a solution of alkali isethionate, alkaliditaurinate, and alkali tritaurinate. Upon the solid-liquid separationof taurine, the mother liquor is directly recycled to the ammonolysisstep.

The advantage of using ammonium isethionate as a starting materialbecomes apparent in that no isolation of alkali salt as a byproduct isnecessary after the separation of crystalline taurine from the motherliquor containing alkali isethionate, alkali ditaurinate, and alkalitritaurinate.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates one embodiment of a flowchart for producingtaurine from ammonium Isethionate.

DESCRIPTION OF THE INVENTION

The present invention relates to a cyclic process for the production oftaurine from ammonium isethionate in a high overall yield of greaterthan 90% to nearly quantitative without generating any inorganic salt asbyproduct.

The starting material, ammonium isethionate is produced by reactingethylene oxide with ammonium bisulfite according to the followingequation:

Ammonium isethionate, produced in a solution, can be used directly forthe production of taurine. Preferably, ammonium isethionate is purifiedby concentrating the solution to obtain crystalline materials. Whensolid ammonium isethionate is used in the production of taurine, thequality of taurine produced is improved and almost no purge of motherliquor is required from the cyclic process.

The process according to the present invention starts with mixing asolution of alkali isethionate or regenerated alkali isethionate, alkaliditaurinate, and alkali tritaurinate, with an excess of ammonia. Thepresence of alkali ditaurinate and alkali tritaurinate in the reactionsolution inhibits the formation of byproducts, increases the productionyield, and greatly reduces or eliminates the waste discharge from theproduction process. The alkali metals are lithium, sodium, or potassium.

The ammonolysis reaction is carried out at a temperature from 160° C. to280° C. under the pressure from autogenous to 260 bars for 1 to 6 hours.

After the ammonolysis reaction, ammonium isethionate is added to theammonolysis solution to react with alkali taurinates. After excessammonia and the ammonia released from the reaction are dispelled fromthe reaction solution and reclaimed for reuse, the pH of the solution orcrystalline suspension is adjusted with an acid to a range of pH 5 to 8.Upon concentrating and cooling, a crystalline suspension of taurine isobtained in a solution of alkali ditaurinate, alkali tritaurinate, andalkali isethionate. The taurine obtained shows no foul smell of ammonia.

The amount of ammonium isethionate in relation to alkali taurinate inthe ammonolysis solution can be from 0.1 to 10 on the molar basis.Preferably, the molar ratio is from 0.5 to 1.5, more preferably from 0.9to 1.1, and most preferably from 0.95 to 1.05. When the ratio is lowerthan the equivalent, the final pH after ammonia removal tends to behigher than 7 and more taurine will remain in the solution. When theratio is greater than equivalent, the final pH is in the desirable rangeof 5 to 6, but additional alkali hydroxide will be consumed during theammonolysis stage.

The reaction of alkali taurinate formed in the ammonolysis stage withammonium isethionate proceeds according to the following equation:

Removal of the excess ammonia and ammonia released from the abovereaction can be effected by heating or by stripping with steam. Aftercomplete removal of ammonia, the strongly basic solution becomes neutralto yield a crystalline suspension of taurine in a solution of alkaliisethionate, alkali ditaurinate, and alkali tritaurinate.

If the ammonia is not completely removed from the solution, the productwill have a slight foul smell of ammonia. In this case, the final pH ofthe solution before crystallization or crystalline suspension of taurinecan also be further neutralized with an acid or passed through an acidicion exchanger to remove trace amount of free ammonia. The final pH is inthe range of 4 to 9, preferably 5 to 8, more preferably 5.5 to 7.5, andmost preferably 6.5 to 7.0. At higher pH than 7, a slight foul smell ofammonia is present in the isolated product of taurine. At a pH lowerthan 5, necessarily extra amount of acid is used in the process.

An acid can be selected from the group of sulfuric acid, hydrochloricacid, hydrobromic acid, nitric acid, phosphoric acid, organic carboxylicacid, and organic sulfonic acid. The acid is preferably isethionic acid,and more preferably, the mixed acids of isethionic acid and ditaurine,produced by bipolar membrane electrodialysis of the mother liquorcontaining alkali isethionate and alkali ditaurinate. The initialsuspension is optionally concentrated, then cooled to crystallizetaurine. Taurine is obtained by means of solid-liquid separation.

The amount of acid used to adjust the final pH of the solution orcrystalline suspension depends on the amount of ammonium isethionateused to react with alkali taurinate. If ammonium isethionate is lessthan equal molar of alkali taurinate, then the solution after removal ofammonia is basic with a pH greater than 7. In general, the sum of acidneeded and ammonium isethionate added is equal to or slightly more thanthe molar equivalent of alkali taurinates in the ammonolysis solution.It is therefore possible to adjust the ratio of ammonium isethionate andisethionic acid/ditaurine mixture, according to the availability themixed acids produced from the bipolar membrane electrodialysis of themother liquor containing alkali isethionate and alkali ditaurinate. Asthe mixed acid is produced in the bipolar membrane electrodialysis, itis therefore preferable to add less than equivalent amount of ammoniumisethionate to react with alkali taurinates, with the balance from themixed acid of isethionic acid and ditaurine.

An added advantage of the current process of using both less thanequivalent ammonium isethionate and isethionic acid/ditaurine is thenearly complete removal of ammonia from the reaction solution at muchhigher pH. The alkaline pH of the solution helps to accelerate theremoval of ammonia from the solution. After complete removal of ammonia,the pH of the solution or crystalline suspension is brought down with asolution of the mixed acids of isethionic acid and ditaurine.

After separation of taurine, the mother liquor, containing regeneratedalkali isethionate, alkali ditaurinate, and alkali tritaurinate, issaturated with ammonia and is subjected to the ammonolysis reaction.

It becomes apparent that alkali in the reaction system is continuouslyrecycled in the process and only ammonium isethionate is transformed totaurine. The net reaction of the cyclic process is:

Useful and effective catalysts for the ammonolysis reaction are foundamong the alkali salts of hydroxide, carbonate, bicarbonate, hydrogensulfate, sulfate, bisulfite, sulfite, nitrate, phosphate, chlorate, andperchlorate. Such salts are sodium hydroxide, lithium hydroxide,potassium hydroxide, lithium carbonate, lithium bicarbonate, sodiumbicarbonate, sodium bicarbonate, potassium bicarbonate, lithiumcarbonate, sodium carbonate, potassium carbonate, lithium sulfate,sodium sulfate, potassium sulfate, lithium phosphate, sodium phosphate,potassium phosphate, lithium sulfite, sodium sulfite, and potassiumsulfite.

The catalyst for the ammonolysis reaction of alkali isethionate in thepresence of alkali ditaurinate and alkali tritaurinate can be onecomponent or a combination of two or more components. Preferablecatalysts are alkali hydroxides and the most preferable catalyst issodium hydroxide.

The amount of the catalyst used is not limited, but is usually from 0.01to 10 in molar ratio of the catalyst to alkali isethionate. The ratio ispreferably in the range of 0.01 to 1, more preferably 0.1 to 0.5, mostpreferably 0.2 to 0.3. A suitable amount of catalyst can be selected bythose skilled in the art for the ammonolysis reaction to complete indesired time.

As a catalyst, alkali hydroxide is introduced into the reaction systemand additional ammonium isethionate is required to neutralize the strongbase. The result is an increased accumulation of alkali in the cyclicprocess. It is thus preferable to generate the alkali hydroxide withinthe production unit as shown in the FIGURE a convenient way is to splitalkali isethionate and alkali ditaurinate in the mother liquor into anacid component, a mixture of isethionic acid and ditaurine, and analkali hydroxide component, by using bipolar membrane electrodialysis.The mixed acid solution of isethionic acid and ditaurine is used as anacid for neutralization and pH adjustment, while the alkali hydroxideproduced is used as a catalyst for the ammonolysis reaction.

The proportion of mother liquor that goes through the electrodialysisprocess can be adjusted according to the need of alkali hydroxide as acatalyst for the ammonolysis reaction and the need of the acidic partfor the neutralization and pH adjustment. The ratio is varied from 1% to50%, preferably from 5 to 30%, most preferably from 10-20%.

The cyclic process according to the present invention affords taurine ina yield of greater than 90%, to nearly quantitative, and generates nowaste other than byproducts of ethylene glycol and monoethanolamine,which are removed from the cyclic process by an extraction process asdisclosed in the co-pending application.

The process according to the present invention can be carried outdiscontinuously, semi-continuously, and continuously.

EXAMPLES

The following examples illustrate the practice of this invention but arenot intended to limit its scope.

Example 1

To a 2-L autoclave were added 1200 mL of 24% ammonia solution, 296 g ofsodium isethionate, and 2 g of sodium hydroxide. The solution was heatedto 260° C. for 2 hours under autogenous pressure. After cooling, 260.0 gof ammonium isethionate was added and ammonia was removed by boiling thesolution to a temperature of 104° C. After cooling to 70° C., a solutionof 65% isethionic acid was added to bring the pH to 6.5. Afterconcentrating and cooling to room temperature, a suspension ofcrystalline taurine was obtained. Taurine was recovered by filtrationand dried to 192.1 g. Taurine is recovered in a yield of 76.8%.

Example 2

To the mother liquor of Example 1 was added 340 g of gaseous ammonia andtotal volume was adjusted to 1500 mL with deionized water, followed byaddition of 12.4 g of sodium hydroxide. The solution was placed in a 2-Lautoclave and was subjected to ammonolysis reaction and treatment withammonium isethionate and a mixture of isethionic acid and ditaurine asdescribed in Example 1.

Taurine, 235.4 g after drying, was obtained in a yield of 94.1% on themolar basis of ammonium isethionate, isethionic acid, and ditaurineintroduced into the reaction solution.

It will be understood that the foregoing examples, drawing, andexplanation are for illustrative purposes only and that variousmodifications of the present invention will be self-evident to thoseskilled in the art. Such modifications are to be included within thespirit and purview of this application and the scope of the appendedclaims.

What is claimed is:
 1. A cyclic process for producing taurine fromammonium isethionate, comprising: (a) adding ammonium isethionate to asolution of a mixture of alkali taurinate, alkali ditaurinate, andalkali tritaurinate to react with alkali taurinates; (b) removingammonia from (a) to obtain a solution or crystalline suspension oftaurine in a solution of alkali isethionate, alkali ditaurinate, andalkali tritaurinate; (c) adding art acid or an acidic ion exchanger toadjust the pH of the solution or crystalline suspension of step (b) to arange from 5 to 9; (d) separating taurine by means of solid-liquidseparation to provide a mother liquor containing alkali isethionate,alkali ditaurinate, and alkali tritaurinate; and (e) adding ammonia orammonium hydroxide to the mother liquor of step (d) and subjecting thesolution to an ammonolysis reaction to produce a solution of a mixtureof alkali taurinate, alkali ditaurinate, and alkali tritaurinate.
 2. Theprocess according to claim 1, wherein the acid is selected from thegroup of sulfuric acid, hydrochloric acid, hydrobromic acid, nitricacid, phosphoric acid, organic carboxylic acids, alkyl sulfonic acids,and aryl sulfonic acids.
 3. The process according to claim 1, whereinthe acid is isethionic acid.
 4. The process according to claim 1, hereinthe acid is a mixture of isethionic acid, ditaurine, and tritaurine. 5.The process according to claim 1, wherein the acid is produced by aprocess of bipolar membrane electrodialysis of a solution of alkaliisethionate or a mixture of alkali isethionate, alkali ditaurinate, andalkali tritaurinate.
 6. The process according to claim 1, wherein anacid is used to adjust the pH of taurine solution or crystallinesuspension to a range of 6 to
 8. 7. The process according to claim 1,wherein the taurine solution is passed through a bed of acidic ionexchanger.
 8. The process according to claim 1, wherein the yield oftaurine from ammonium isethionate is from 90% to nearly quantitative. 9.The process according to claim 1, wherein the alkali metals are lithium,sodium, or potassium.